YARMOUTH, Maine — Rosalie Baker-Brown fired the starting gun at the Boston Marathon on Monday, something she has done many times since the mid-1990s.

Now 85, Baker-Brown has been intimately involved in the race for decades. She grew up in Hopkinton, Mass., where the marathon begins, and married into the Brown family, which helped found the race.

On Monday, the Yarmouth resident was happy to see the 117th annual marathon start without a hitch.

“When you see 23,000 runners go by it’s thunderous and yet the spirit is terrific,” Baker-Brown said Tuesday. “You know, I told [my son] this is almost a perfect day. The weather was the perfect condition for running. There was no tailwinds, or winds of any kind. It was a comfortable 50 degrees, not hot like last year.”

But the perfect day came to an abrupt end when two bombs rocked Boylston Street in downtown Boston, killing three people and injuring at least 170.

Baker-Brown watched as her granddaughter, Caity Gildart, of Portland, the sales and marketing director for Casco Bay Lines, began her second Boston Marathon, and expected to find her at the finish line a few hours later.

But around Mile 13, Gildart dropped out of the race from a knee injury and overall exhaustion. She headed for a bus that was transporting injured and fatigued runners to the finish line.

“We were in a school bus headed for the medical tent when I heard the first explosion,” Gildart said, noting they were about a block and a half from the explosions, driving on a street parallel to Boylston Street where the bombs went off.

The bus pulled up to the medical tent and Gildart watched as the grisly scene unfolded.

“We saw people running toward the medical tent from the finish line,” she said. “There were rumors that the grandstands had collapsed. No one knew what was going on. Technically, we weren’t supposed to get off the bus until we were cleared, but at that point it was just sort of mayhem.”

The energy in the area was tense, Gildart said, with people scrambling to find friends and relatives. “The Boston Marathon is one of the most well-organized and heavily-volunteered events in the country,” she said, “and it was chaos.”

Baker-Brown, who typically volunteers in the wheelchair division and often heads to the finish line to cheer on family and friends as they cross, said this year she decided to hang around the starting line.

She and her family immediately began to wonder what happened to her granddaughter, not knowing she had dropped out of the race.

Eventually, Gildart met up with her husband and friends and let her family know she was safe, she said.

Baker-Brown said they were relieved to hear from Gildart.

“We were just trying to make sure everyone was alright,” she said. “I think that’s how we are as a people, and I hope that doesn’t change.”

Gildart said after leaving the bus she was eventually able to regroup with her husband and friend, who had been at about Mile 25 of the 26.2-mile race when the explosions went off.

Before Monday, Gildart said she had vowed to never run another marathon, thinking she was only going to volunteer this year in Boston. But, instead she decided to run.

She said Monday’s terror attack won’t prevent her from being a spectator again.

“A couple of my running mates texted each other this morning and we’re sort of glad we were all part of it together,” Gildart said. “We can now appreciate knowing each other, and now we appreciate our husbands, families and kids more. I hope it doesn’t have a big effect in the future and that people feel safe enough to go to events like this.”

Baker-Brown said even before Monday’s tragedy that this would likely be the last time she started the marathon. Throughout the years, she said, she has watched the race in several different capacities, including as a child growing up in the area.

“I came from Hopkinton. I’m a local girl and it meant a lot to me that my father had taken me to the race 80 years ago,” she said. “I had always liked being at the start and then going to the finish line to watch.”

Now the race — which, Tom Brown, her deceased husband, used to oversee as the president of the Boston Athletic Association — is blemished by tragedy.

“I know we’re a stoic group of people,” she said, adding that the marathon has always filled the streets of Boston with families. “It’s still exciting and still a family day and that’s why what happened yesterday was so tragic.”

She said her late husband’s family began the race because they believed in having a race for not only elite athletes, but for everyday lovers of sport.

Now, she said, it’s forever changed.

“I wonder how the Brown men would think of their amateur race now?” she said. “Certainly it’s a special race and this is an awful way to dim the race and the impact that it has had. Hopefully the families impacted by this event will recover. … This was a perfect day, until some fool planted a series of bombs.”